Various construction for a rolling bearing unit with a rotational speed detector for supporting a wheel by the suspension of an automobile so as to be able to rotate freely, and for determining the rotational speed of that wheel has been known previously. In the case of any of the conventional construction, a detecting section of a sensor that is supported by and fastened to a non-rotating portion is made to face a detected surface of an encoder that is supported by and fastened to part of a hub that rotates together with the wheel. In this construction, the rotational speed of the wheel that rotates with the encoder is found based on the frequency or period of an output signal from the sensor that changes as the encoder rotates.
In order to protect the encoder of this kind of rolling bearing unit with a rotational speed detector from damage due to muddy water or dust adhering to the encoder, or, in order to prevent foreign matter such as magnetic powder from adhering to the encoder and damaging the reliability of the rotational speed detector that uses the encoder, construction such as disclosed in JP 4206550 (B2) and DE 19644744 (A1) of separating the encoder from the outside by a cover made of a non-magnetic plate is conventionally known. FIG. 11 illustrates an example of conventional construction as disclosed in JP 4206550 (B2). This conventional construction comprises a rolling bearing unit 2 with an encoder in which an encoder 1 is assembled, and a sensor 4 that is supported by and fastened to a knuckle 3 of the suspension.
In the rolling bearing unit 2 with encoder, the encoder 1 is supported by and fastened to the inside end section in the axial direction of the hub 6 of the rolling bearing unit 5 so as to be concentric with the hub 6. In addition to the hub 6, the rolling bearing unit 5 comprises an outer ring 7 and a plurality of rolling elements 8. The outer ring 7 has double rows of outer ring raceways 9 around the inner circumferential surface and a stationary flange 10 on the outer circumferential surface. During operation, the outer ring 7 is supported by the knuckle 3 and does not rotate.
The hub 6 comprises a main hub body 11, and an inner ring 12 that is connected and fastened to the main hub body 11 by a crimped section 13 that is formed on the inside end section in the axial direction of the main hub body 11; the hub 6 having double rows of inner ring raceways 14 around the outer circumferential surface thereof, and being supported on the inner-diameter side of the outer ring 7 so as to be concentric with the outer ring. Moreover, a rotating side flange 15 for supporting the wheel is provided on the outside end section in the axial direction of the main hub body 11 in the portion that protrudes further outward in the axial direction than the opening on the outside end in the axial direction of the outer ring 7. The rolling elements 8 are located between both outer ring raceways 9 and both inner ring raceways 14, with the rolling elements supported by a cage 16 in each row, so as to be able to roll freely. Furthermore, both end sections in the axial direction of the internal space 17 where the rolling elements 8 are located are covered by a seal ring 18 and a cover 19. In this specification, the “outside” in the axial direction is the side toward the outside in the width direction of the vehicle when assembled in the suspension. On the other hand, the “inside” in the axial direction is the side toward the center in the width direction of the vehicle when assembled in the suspension.
The cover 19 is formed using a non-magnetic metal plate such as an aluminum alloy plate, or austenitic stainless steel plate, or some other non-magnetic material. This kind of cover 19 comprises a cylindrical section 20 that extends in the axial direction, and a flat plate section 21 that is bent and extends inward in the radial direction from the inside end section in the axial direction of this cylindrical section 20. In the construction in FIG. 11, the rolling bearing unit 5 is applied to a non-driven wheel (rear wheel for a FF vehicle, front wheel for a FR vehicle or MR vehicle), so the flat plate section 21 is a circular plate shape that covers the entire opening on the inside end in the axial direction of the outer ring 7. On the other hand, in the case of a rolling bearing unit for a driven wheel (front wheel for a FF vehicle, rear wheel for a FR or MR vehicle, and any wheel for a 4WD vehicle), in the construction disclosed in DE 19644744 (A1), the flat plate section is ring shaped in order that the drive shaft can be inserted to the inner-diameter side of the cover. In either case, the cover 19 is such that the cylindrical section 20 fits inside the inside end section in the axial direction of the outer ring 7 with an interference fit, and is fastened to this inside end section in the axial direction of the outer ring 7.
The base end section of the encoder 1 is fitted onto a shoulder section 22 that is formed on the inside half in the axial direction of the inner ring 12, which corresponds to a portion toward the inside end of the hub 6, so that the encoder 1 is concentrically supported by and fastened to the hub 6. The encoder 1 comprises a support ring 23 that is formed into a circular ring shape with an L-shaped cross section by bending a magnetic metal plate such as low carbon steel plate, and a main encoder body 24 that is made using a permanent magnet such as a rubber magnet. This main encoder body 24 is magnetized in the axial direction, and by alternating the magnetization direction at uniform intervals in the circumferential direction, S poles and N poles are alternated at uniform intervals on the inside surface in the axial direction, which is the detected surface. The detected surface of this kind of main encoder body 24 is made to closely face through a small gap the outside surface in the axial direction of the flat plate section 21 of the cover 19 (surface on the internal space side). In other words, the cover 19 is pushed onto the inside end section in the axial direction of the outer ring 7 until the outside surface in the axial direction of the flat plate section 21 closely faces the detected surface of the main encoder body 24.
Furthermore, with the sensor 4 supported by and fastened to the knuckle 3, the detecting section of the sensor 4 is brought into contact with the inside surface (surface on the outer space side) in the axial direction of the flat plate section 21. In the state, the detecting section faces the detected surface of the main encoder body 24 by way of the flat plate section 21. In this state, as the main encoder body 24 rotates together with the hub 6, the S poles and N poles on the detected surface come by near the detecting section of the sensor 4 alternately, which causes the output of the sensor 4 to change. The frequency of this change is proportional to the rotational speed of the hub 6, and the period of this change is inversely proportional to the rotational speed, so based on either or both the frequency and period, the rotational speed of the wheel that is fastened to the hub 6 is found.
In the case of the conventional construction illustrated in FIG. 11, the permanent magnet main encoder body 24 and the external space are separated by the non-magnetic cover 19, so it is possible to prevent foreign matter such as magnetic powder from adhering to the detected surface of the main encoder body 24. As a result, this detected surface is maintained in a clean state, making it possible to maintain reliability of the rotational speed detector that uses this main encoder body 24. However, there is a need to improve the precision related to the distance between the detected surface of the main encoder body 24 and the detecting section of the sensor 4.
In other word, when the cylindrical section 20 is fitted inside the inside end section in the axial direction of the outer ring 7 with an interference fit in order for the cover 19 to be supported by and fastened to the outer ring 7, a force is applied in a direction inward in the radial direction to the flat plate section 21 that is on the inner-diameter side of the cylindrical section 20. Particularly, in the case of this conventional construction, the radius of curvature of a bent section that exists at the continuous section between the outer circumferential edge of the flat plate section 21 and the edge on the inside end in the axial direction of the cylindrical section 20 is small (in other words, bent with large curvature), and the portion that fits inside and is fastened to the outer ring 7 with an interference fit extends to nearly the outer circumferential edge of the flat plate section 21. Therefore, the force inward in the radial direction that is applied to the flat plate section 21 becomes considerably large, and due to this force the flat plate section 21 deforms in the direction of thickness (inward and outward in the axial direction) so as to curve.
The deformation direction and the amount of deformation cannot be regulated or predicted, so the position in the axial direction of the portion on the flat plate section 21 between the detected surface of the main encoder body 24 and the detecting section of the sensor 4 cannot be regulated with good precision. For example, when the sensor 4 is positioned by the detecting section of the sensor 4 coming in contact with the inside surface in the axial direction of the flat plate section 21 (surface on the external space side), that positioning become inaccurate when the flat plate section 21 is distorted. As a result, there is fluctuation in the density of the magnetic flux that reaches the detecting section of the sensor 4 from the detected surface of the main encoder body 24, which is disadvantageous from the aspect of maintaining the reliability of the rotational speed detection.